ADUs are allowed in Unincorporated JeffersonTypes:DetachedInternal
Types:DetachedInternal
Accessory Dwelling Unit (ADU) Rules for Unincorporated Jefferson, CO
Is your property eligible for an ADU?
# of Properties
74,296
Owner-occupied
78%
Zoning districts
63
Avg Home Value
$816,550
Median Lot Size
0.24 acres
Avg Income
$144,913
Residential Types:
74,296 housing units
Single Family
8%
Apts (4+ units)
5%
Other
87%
Zoning Districts:
100,444 parcels · 63 districts
P-D
51%(51,271)
A-2
11%(10,774)
MR-1
10%(9,703)
R-1A
5%(5,051)
Other
24%(23,645)
ADU Rules
What can you build in Unincorporated Jefferson, CO?
Unincorporated Jefferson, CO follows state and local rules for Accessory Dwelling Units. Here is a concise overview of the local rules.
Eligibility
- –Internal / Attached ADU: By Right
- –Detached ADU: By Right
Interior / Attached ADU Size Limits
- –Maximum of 1,200 sq ft or 40% of the primary dwelling’s total floor area (including basements but excluding garages), but never less than 500 sq ft; basement conversions are exempt from this cap.
Detached ADU Size Limits
- –Maximum detached ADU size by lot: 600 sq ft (≥7,500 sf), 800 sq ft (≥12,500 sf), or 1,200 sq ft (≥1 acre), further limited to 40% of the primary dwelling’s floor area with a 500-sq-ft floor; none allowed on lots under 7,500 sq ft; and total accessory uses also cannot exceed the primary dwelling’s floor area.
Max Units
- –1 ADU per single-family detached lot
- –0 ADUs per lot for duplex/two-family and multifamily
Owner Occupancy
- –Owner must occupy the property as their primary residence.
Parking
- –1 space per bedroom; no maximum; ADU must use the same driveway as the primary dwelling; no transit-based waivers
Rental Restrictions
- –STRs in ADUs require a County STR License; one license per property; no simultaneous STRs; 750-ft separation; 1% cap by Fire Protection District; if an STR is used, up to 3 occupants and the on-lot SFH must be the owner’s primary dwelling.
ADU State Law
What can you build in Colorado?
- –ADUs must be approved based on objective standards; no discretionary hearings allowed.
- –Historic properties: Local historic review may still apply in designated historic districts.
- –Exempt parcels: ADUs are not required to be allowed on parcels without adequate water/sewer, in floodways, or on certain historic properties.
- –HOAs cannot prohibit ADUs: HOA rules that conflict with the state ADU law are void.
- –Parking exceptions exist: In rare cases, one parking space may be required if there is no existing off-street parking and on-street parking is prohibited.
- –Local rules still matter: Building code, fire code, utility capacity, and life-safety standards still apply.
- –More permissive is allowed: Municipalities may allow larger ADUs, multiple ADUs, or additional housing types beyond what the state requires.
- –Local zoning controls whether ADUs are allowed at all.
- –HOA rules may still apply.
- –More permissive local rules are allowed.
What's allowed on your lot?
These are the municipality-wide rules. What's allowed on a specific property also depends on state laws, setbacks, floor area ratio, lot coverage, environmental constraints, topography, and other property-specific factors. Search your address on FutureLot to see what's allowed on your property.
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ADU rules in other Colorado municipalities
Rules change at the town line. Check the municipality your property is actually in.
Jefferson County